Scatter Theory and Analysis

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Results and Discussion

NEW SPIE paper on HEG scatter: Scattering Model (1.6 Mb .ps)

(Updated 10/21/97 dd)

The HEG scatter is one of the few surprises from the HETG at XRCF. The size of the scatter is small enough that for most purposes it is a curiosity more than a crucial ingredient in HETG data analysis. The state of scatter analysis is shown by the plot below (.ps version) and these reduced, normalized 1.775 keV data are available in an .rdb format file.

The "grating mystery" section here summarizes the history of this phenomenon.

#4 HEG scatter at 1.775 keV - Case almost Closed

Herman's scattering test (monochromator with W line) shows scatter along the dispersion direction, possibly concentrated in two peaks (containing 0.5 % of the line flux?) to either side of the (cusp-occulted) main line. What's the origin of these scattered photons?

TOGA-HEG scatter seen in XRCF Phase 1 rehearsal

• Jeremy's note on the test
• Jan.30 1997: shows up at XRCF with flight HETG at level of 0.38% for HEG and not for MEG gratings. Not at zero order and probably not at 4.5 keV either.
• '2C data taken at end of Phase 2G shows HEG scatter at all orders and no scatter on MEG:

  • G-H2C-SC-88.001	G-H2C-SC-88.002	G-H2C-SC-88.003	G-H2C-SC-88.004	G-H2C-SC-88.005
    Zero-order	MEG+1, HEG+1	HEG+1, MEG+3	HEG+2/MEG+4, MEG+5	MEG+5, HEG+3

  • Doing a PHA on the scattered and non-scattered photons selected from all photons in the '88.002 data shows that the scattered energy is the same as the 1.775 line (e.g., true scattering).
  • Herman's Analysis of the 2C scattering data which lead to the normalized plot and data file available above.
• Scatter theory memos:
  • "Grating Scatter due to ...(.ps.gz)" by John Davis - indicating that the "0.5%" can be explained qualitatively by grating bar variations and their scatter: a few percent of a period jitter in bar width can put of order 0.5% into scatter.
  • "Scattering by Transmission Gratings...(.ps.gz)" by Frits Paerels